The milk ejection reflex is a lactation reflex triggered by the infant sucking on the maternal breast. The registered touch causes milk to shoot into the breast. Disorders of the reflex are either due to a deficiency of the hormone involved, oxytocin, or are associated with neurologic disorders.
What is the milk ejection reflex?
The milk ejection reflex is a lactation reflex that is triggered by the infant sucking on the maternal breast. The so-called lactation reflexes are common reflexes across species that are triggered by the offspring sucking on the maternal breast. In addition to the lactation reflex, the milk ejection reflex is also one of the reflexes in this group. The triggering stimuli are always touch stimuli. Thus, mechanoreceptors registering touch are the first instance of the reflex arc. The lactation reflexes are extraneous reflexes whose effectors and affectors are located in different organs. The purpose of the reflexes is to secure food for the newborn. Not only the female breast, but also the teat of animals has reflexes of lactation and ejection. Basically, milk formation is a closed unit with milk ejection, since the ejection reflex cannot take place without the milk formation reflex. Both are combined with all the processes involved in them under the term lactation. Accordingly, lactation is the reflective formation and secretion of breast milk by the female mammary gland.
Function and task
Lactation encompasses physiologic processes that extend from the onset of pregnancy through the lactation period. For lactogenesis in pregnancy, in addition to the hormone estrogen, progesterone, HPL and prolactin play a crucial role. From the second month of pregnancy, the proportion of fat and connective tissue within the breast decreases. From the eighth month, galactogenesis occurs, during which the production of breast milk begins and the formation of foremilk starts. Prolactin continues to increase in concentration during pregnancy and initiates the formation of foremilk. Full breast milk is formed only after the birth of the child, when the placenta is discharged. The placenta forms progesterone, which partially occupies the receptors for prolactin during pregnancy and thus inhibits them. The onset of lactation begins. After the birth of the child, the interaction between the mother and the newborn child is the crucial element for both milk production and ejection. All lactation reflexes are tied to this interaction. The stimulus of touch on the mechanoreceptors of the maternal breast results in the release of prolactin during breastfeeding. This hormone originates from the anterior pituitary gland and causes an increase in milk production in the female mammary glands. This reflex corresponds to the milk-forming reflex. At the same time, breastfeeding with the same reflex arc triggers the ejection reflex. This milk ejection or milk-giving reflex is thus also caused by the suckling of the offspring at the mother’s breast and stimulates the release of milk. As for the lactation reflex, the stimulation of the nipple and the registration of the stimulation by the mechanoreceptors located there is the crucial element of the reflexive processes. The sensitive nerve fibers transmit the sucking stimuli to the mother’s hypothalamus, which initiates a release of the peptide hormone oxytocin in the posterior pituitary in addition to the release of prolactin. While prolactin stimulates milk production, oxytocin stimulates myoepithelial cells in the mammary glands to contract. This contraction transports the milk produced from the alveolar end chambers to the cisterns of the mammary gland, which are the collection spaces for the milk. The time between stimulation of the breast by the infant and the injection of milk into the burst is approximately ten seconds.
Diseases and ailments
The milk ejection reflex is dependent on the peptide hormone oxytocin. For this reason, an absolute deficiency of oxytocin causes the reflex to fail. Such a deficiency may be due to pituitary insufficiency. Specifically, posterior pituitary insufficiency leads to isolated failure of the neurohypophysis. The result is impaired secretions of ADH and oxytocin. One of the most frequent causes of pituitary insufficiency is tumors of the pituitary gland.As soon as a tumor presses on the endocrine gland, hormone production fails. Insufficiencies can also exist after surgery on the pituitary gland. Not only a deficiency of oxytocin, but also a deficiency of prolactin can lead to disorders of the milk ejection reflex. Since prolactin supports the formation of milk, a deficiency leads to decreased milk production. If there is too little milk, correspondingly less milk can be ejected. A prolactin deficiency is also usually due to an underactive hormone gland. Disorders of the milk ejection reflex may also be due to damage to the afferent nerve pathways by which the mechanoreceptors communicate with the hypothalamus. Such nerve damage can be caused by mechanical injury as well as by infection, inflammation, or deficiency. Either the peripheral nerves in the corresponding region are affected or the damage is in the central nervous system. For damage to the peripheral nerves, the term neuropathy applies. If the lesions are located in the central nervous system or even in the hypothalamus, neurological diseases may be the primary cause of the impaired reflex arc. The same is true for CNS tumors, strokes, or traumatic brain injury. Unlike an absent milk ejection reflex, a diminished milk ejection reflex does not necessarily have disease value. For one thing, the amount of milk production differs from woman to woman and may also be influenced by diet, for example, and furthermore, natural differences in reflex activity exist from person to person.
